Fluorine-containing resins such as homopolymer or copolymers of tetrafluoroethylene have a very low surface energy in comparison with other resins, and therefore have an extremely superior surface properties such as water- and oil-repelling property, non-tackiness and mold-releasing property. In addition, it has been known that because of their chemical stability, they have many excellent properties such as chemical resistance, corrosion resistance and heat resistance, and thus the fluorine-containing resins have been applied to wide and various fields.
The fluorine-containing resins, however, have problems that they are easy to be electrostatically charged, because they are electrically insulative.
For example, in computer devices and various office automation (O.A.) machines, electronic parts such as IC and LSI and magnetic storages must be protected from electrostatic charge and sparks due to the charge. Therefore, for the parts to be used for their peripheral equipments or business machines (e.g. bearing parts for various rollers and transferring machines) are required a sufficient antistatic property.
Further, for a reservior of chemicals and an equipment used in preparation process of semiconductors, but for a sufficient antistatic property, not only the elements are broken due to the electrostatic charge, but also the maintenance of clean environment is obstructed.
Moreover, a fluorine-containing resin film is used as an offset-preventing layer for the surface of a fixing roller in a heat roller fixing equipment of electrostatic copying machines. In this case, when using the fluorine-containing resin alone, though non-tackiness and mold-releasing property to a toner melted by heating (hereinafter referred to as "hot-offset-preventing effect") are sufficient, there arises the problem of a phenomenon so-called electrostatic offset, that is, due to the abrasion between the fixing roller and paper sheets the offset-preventing layer of the fluorine-containing resin is charged gradually, and then the toner before fixing is electrostatically adsorbed or repelled, which results in blotting and missing in electrostatic images.
Further, in view of saving energy and shortening a warm-up time of machines it is desired to carry out the fixing at a temperature as low as possible. For this purpose, a fixing roller having an excellent heat conductivity is desired. Accordingly, it is required that the offset-preventing layer is made as thinner as possible and also has abrasion resistance together with the above various properties.
In order to solve the above problems, there has been proposed a composition of a fluorine-containing resin with which various electrically conductive fillers are blended.
For example, JP-B-38302/1991 discloses a fluorine-containing resin composition to which a carbon black is added as the electrically conductive filler. When adding the electrically conductive carbon black to the fluorine-containing resin, the composition is endowed with an electric conductivity and thus an excellent antistatic ability can be achieved. However, since the electrically conductive carbon black has a larger surface energy than the fluorine-containing resin, the carbon black is inferior to the fluorine-containing resin in such properties as water- and oil-repelling property, non-tackiness and mold-releasing property. Accordingly, the composition of the fluorine-containing resin and the electrically conductive carbon black has the problem that the composition is inferior to the fluorine-containing resin used alone in such properties as water- and oil-repelling, non-tackiness and mold-releasing property, and therefore such a composition has been practically used within the limited use.
To the offset-preventing layer of the fixing roller, it has been also tried to add various electrically conductive fillers.
For example, JP-B-23626/1983 proposes the use of a resin layer containing a carbon black and the like as the offset-preventing layer. When an addition amount of carbon black is made larger, a volume specific resistivity can be lowered, which results in improvement of electrostatic offset-preventing effect. However, the hot offset-preventing effect becomes bad. In order to solve this dilemma, in the practical application there is obliged to use a wet process in which a silicone oil is applied to the surface of the fixing roller.
JP-B-59468/1990 proposes the addition of a carbon fluoride to a fluorine-containing resin together with a carbon fiber as the electrically conductive filler in order to compensate the hot offset-preventing effect. In this case, though the both offsets, i.e. hot-offset and electrostatic-offset can be prevented, it is difficult to form uniformly an offset-preventing layer containing the two fillers. When the surface of the offset-preventing layer is uneven, it is impossible to maintain the offset-preventing effect for a long time.
As explained above, in the practical situation, it is difficult to prepare a fluorine-containing resin molded article which has a uniform surface and is simultaneously sufficient in both of antistatic ability and non-tackiness.
The present invention has been made on the basis of those problems, and has an object to provide a fluorine-containing resin molded article with an excellent antistatic ability and non-tackiness due to its proper electric conductivity and sufficiently low surface energy.
Another object of the present invention is to provide a novel process for preparing a fluorine-containing resin molded article with an antistatic ability and non-tackiness.
Further object of the present invention is to provide a fixing roller for electrostatic copying machine having a high offset-preventing ability, and to provide a preparation process of the same.